TS-2469: remove libreadline which is gpl licensed

Signed-off-by: Zhao Yongming <ming.zym@gmail.com>

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TS-2467: traffic_shell doesn't work with tcl 8.6, works with 8.5

Segfault in libtcl8.6.so when calling Tcl_SetMainLoop(Tcl_ReadlineMain).
If setting Tcl MainLoop, we should call Tcl_FindExecutable(NULL),
which fixes TCL 8.6 and should also work with older versions.

Conflicts:
	CHANGES